1. Field of the Invention
The present invention relates to a comparator circuit, more particularly, to a comparator circuit using a resonant-tunneling transistor (RTT). This resonant-tunneling transistor has a resonant-tunneling barrier for injecting electrons, which includes a resonant-tunneling hot-electron transistor (RHET) and a resonant-tunneling bipolar transistor (RBT).
2. Description of the Related Art
Generally,, a comparator circuit comprises a differential amplifier and a plurality of transistors. The differential amplifier is supplied with an input signal and a reference signal and compares the input signal and the reference signal, and the transistors of the comparator circuit are supplied with a clock signal for outputting a digital signal from an output signal of the differential amplifier. When the input signal is lower than the reference signal, a low level clock signal is output from the comparator circuit, and when the input signal is higher than the reference signal, a high level clock signal is output from the comparator circuit. That is, the change of the output pulse of the conventional comparator circuit can be produced by a small difference in level between the input signal and the reference signal.
However, the conventional comparator circuit has several problems; for example, the conventional comparator circuit needs a plurality of transistors, such as traditional bipolar transistors or field effect transistors, and thus the configuration of the conventional comparator circuit tends to become complex and the operation speed thereof is too slow. Further, the conventional comparator circuit also needs the clock signal for outputting the output pulse from a small difference in level between the input signal and the reference signal, and therefore, the output signal of the conventional comparator circuit is not output until the clock signal has changed. The problems of the conventional comparator circuit will be later explained in detail.
Note, recently a resonant-tunneling transistor having a resonant-tunneling barrier for injecting electrons has been developed. This resonant-tunneling transistor includes a resonant-tunneling hot-electron transistor and a resonant-tunneling bipolar transistor, and has negative differential resistance characteristics and a high speed operation. These resonant-tunneling transistors are shown in U.S. patent application Serial No. b 937,615 and U.S. Pat. No. 4,712,121.